The Space Platform for Checking Aggression is a military orbital weapons platform.

The Space Platform was new at the time of the novel. It housed a New Weapon that made the H-bomb obsolete. When used, it would create a "pyre in the characteristic shape of an artichoke."

We had arranged a radio hookup with the space platform, a gadget the Army had succeeded in establishing six hundred miles up, in the regions of the sky beyond the pull of gravity. The army, after many years of experimenting with rockets, had not only got the platform established but had sent two fellows there in a Spaceship, and also a liberal supply of the New Weapon.

The whole civilized world had read about this achievement, which swung the balance of power so heavily in our favor, and everyone was aware that the damned platform was wandering around in its own orbit at a dizzy distance from the Earth and not subject to gravitational pull.

As far as I know, this is the first use of the phrase "space platform," and a very early description of the idea of an orbital weapons platform.

The Salyut space stations launched in the early 1970's by the USSR were the first manned artificial satellites in orbit. The Marshall Space Flight Center worked on what it called the "Science & Applications Space Platform" (SASP) in the late 1970's. MSFC envisioned a series of relatively “platforms” for different missions.

In the 1980's, President Reagan proposed the Strategic Defense Initiative (SDI); it was originally designed as orbital anti-ICBM defense system in which a laser would intercept incoming ICBMs as they would approach high altitudes. This proposal was later scrapped in favor of ground-based systems.

At present, the Outer Space Treaty (in force since 1967) and the Strategic Arms Limitations Treaty II (SALT II - in force since 1979) prohibit the placement of weapons of mass destruction in space.